During the conversion of carcinogenic amines and nitro compounds to excretable metabolites in liver cells, reactive electrophilic species are generated that can bind to protein and nucleic acids, and may thereby induce neoplasia. A common metabolite of both amine oxidation and nitro reduction, the arylhydroxylamine (AH), has been postulated as the proximal carcinogen. The major objectives of the research outlined in this proposal are: (1) the development of rapid, sensitive, and accurate electroanalytical methods for the quantitative determination of AHs directly in tissue homogenates, organ perfusion systems and intact animals; (2) to determine whether AHs derived from carbocyclic aromatic amines and heteronuclear aromatic nitro compounds (4-nitroquinoline-l-oxide (NQO)) are metabolized through a common pathway, generating common electrophilic intermediates; and (3) to determine if enzymatic decomposition of these AHs occur with the formation of free-radical or ionic intermediates. 4-Nitroquinoline-l-oxide, carbocyclic aromatic amines (2-aminofluorene and 1-nitronaphthalene) or their corresponding hydroxylamines will be incubated with metabolizing enzyme systems and the influence of esterifying enzymes and free radical stimulators and quenchers on AH formation and turnover will be determined electrochemically. Substituted AHs that can trap nitrogen radicals and nitrenium ions will be incubated with metabolizing enzymes and studied in chemical systems as well. Substituents will be chosen that react differently with radicals (at different sites or at different rates) than they do with ionic intermediates. Mechanism of N-O bond cleavage (ionic vs. radical) may then be elucidated from examination and comparison of the products isolated from chemical and enzymatic systems.